整理

include/boost/iterator/advance.hpp

@@ -0,0 +1,74 @@
+// Copyright (C) 2017 Michel Morin.
+//
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_ITERATOR_ADVANCE_HPP
+#define BOOST_ITERATOR_ADVANCE_HPP
+
+#include <boost/config.hpp>
+#include <boost/iterator/iterator_categories.hpp>
+
+namespace boost {
+namespace iterators {
+namespace detail {
+
+template< typename InputIterator, typename Distance >
+inline BOOST_CXX14_CONSTEXPR void advance_impl(InputIterator& it, Distance n, incrementable_traversal_tag)
+{
+    while (n > 0)
+    {
+        ++it;
+        --n;
+    }
+}
+
+template< typename BidirectionalIterator, typename Distance >
+inline BOOST_CXX14_CONSTEXPR void advance_impl(BidirectionalIterator& it, Distance n, bidirectional_traversal_tag)
+{
+    if (n >= 0)
+    {
+        while (n > 0)
+        {
+            ++it;
+            --n;
+        }
+    }
+    else
+    {
+        while (n < 0)
+        {
+            --it;
+            ++n;
+        }
+    }
+}
+
+template< typename RandomAccessIterator, typename Distance >
+inline BOOST_CXX14_CONSTEXPR void advance_impl(RandomAccessIterator& it, Distance n, random_access_traversal_tag)
+{
+    it += n;
+}
+
+} // namespace detail
+
+namespace advance_adl_barrier {
+
+template< typename InputIterator, typename Distance >
+inline BOOST_CXX14_CONSTEXPR void advance(InputIterator& it, Distance n)
+{
+    detail::advance_impl(it, n, typename iterator_traversal< InputIterator >::type());
+}
+
+} // namespace advance_adl_barrier
+
+using namespace advance_adl_barrier;
+
+} // namespace iterators
+
+using namespace iterators::advance_adl_barrier;
+
+} // namespace boost
+
+#endif